Spool-type valves for controllably diverting the flow of fluids are well known. In a typical spool valve, a piston or “spool,” having a plurality of annular grooves in the spool wall is slidably disposed within a cylindrical body that is also provided with a plurality of internal annular grooves and radial ports extending through the body wall. The spool is variably positionable axially within the body to cause selected ports in the spool to align with grooves and ports in the body, thereby permitting flow of fluid from outside the body through first aligned ports into the interior of the spool and out through second aligned ports. A plurality of different flow paths typically is created by positioning the spool at a plurality of different axial positions within the body. Typically, the spool is connected to a linear solenoid actuator, whereby the spool may be axially positioned by signals from a controller such as a computerized engine control module, although other actuators such as pneumatic and hydraulic actuators can be used.
A common usage for an oil-control spool valve is to variably actuate engine control subsystems such as camshaft phasers, variable valve activation (VVA) mechanisms, and multi-step or valve deactivation mechanisms. In a two step valve mechanism, for example, the mechanism selects the engine intake valve lift profile (low or high) of an intake valve camshaft using a hydraulically activated roller finger follower (RFF).
In a simple configuration of this example, a spool valve supplies high pressure oil, typically from an engine-driven oil pump, to activate the RFF, and shuts off the oil supply to deactivate and drain pressure from the RFF. However, it is desirable that in RFF-deactivation mode the oil supply not be completely shut off, as other components of the valve train, such as camshaft lobes and rocker arms, continue to require flow of oil for lubrication.
U.S. Pat. No. 6,904,937 discloses a piloted spool-type valve that is switchable not simply between on and off modes but also between a pressure high enough for RFF activation and a controlled pressure sufficient for lubrication but insufficient for RFF activation. A piloted spool-type valve requires two spools to function; a regulating spool and a pilot spool. The regulating spool controls a relatively high flow of working fluid through the valve by being axially displaced in the valve. A high force is required to axially displace the regulating spool because of the high hydraulic force acting on the regulating spool as a result of the high flow of working fluid being directed by the regulating spool. The force required to axially displace the regulating spool is higher than can practically be supplied by a mechanical actuator. The pilot spool is therefore provided to be axially displaced in the valve in order to direct a low flow of working fluid which in turn axially displaces the regulating spool. A mechanical actuator can provide the force needed to axially displace the pilot spool in the valve since the pilot spool is subjected to a smaller hydraulic force from the working fluid because of the low flow of working fluid being directed. While a piloted spool-type valve works well in an application with a relatively high flow requirement, a piloted spool-type valve adds unnecessary complexity and expense when used in an application that has lower flow requirements and thus produces lower hydraulic forces on the regulating spool.
U.S. patent application No. 12/718,013 filed on Mar. 5, 2010 and commonly assigned to Applicant discloses a direct acting, i.e. non-piloted, oil control valve assembly that is switchable not simply between on and off modes but also between a pressure high enough for RFF activation and a controlled pressure low enough for lubrication but insufficient for RFF activation. In this example, the control port is arranged to extend radially outward from the oil control valve assembly while the vent port is fed by a passage that extends axially through the spool. However, some applications exist where an oil control valve assembly with a control port that extends axially outward therefrom is needed. The vent path of Ser. No. 12/718,013 may make it difficult to apply an axially extending control port thereto.
What is needed is a simpler, direct-acting, i.e. non-piloted, oil control valve assembly that is switchable not simply between on and off modes but also between a pressure high enough for RFF activation and a controlled pressure low enough for lubrication but insufficient for RFF activation. What is also needed is such an oil control valve assembly with a control port that extends axially therefrom.